Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Segment Reporting Information [Line Items]
Average Assets	$ 123,897	$ 101,780	$ 97,345
Business Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	5,442	5,339	5,321
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	25,363	24,143	24,041
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Average Assets	20,571	18,827	18,632
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Average Assets	41,253	26,648	23,153
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	2,578	2,918	3,007
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average Assets	11,739	11,035	10,912
All Other [Member]
Segment Reporting Information [Line Items]
Average Assets	$ 16,951	$ 12,870	$ 12,279